An electronic apparatus is a device including a circuit substrate having signal lines and a plurality of semiconductor packages mounted on the circuit substrate. Signals propagating through the signal lines formed in the circuit substrate are input into and output from the semiconductor packages.
The circuit substrate is a board including glass cloth and a thermosetting resin impregnated into the glass cloth. The permittivity of glass cloth is not constant, and varies in the circuit substrate. Accordingly, when a signal propagates through a signal line, the permittivity is changed depending on the position of the signal line in the circuit substrate.
An electronic apparatus in which variations in the signal propagation time are reduced by providing signal lines in a polyimide film and by allowing signals to be transmitted through the signal lines has been proposed.
A polyimide film is a flexible insulating film. A polyimide film in which signal lines are provided (hereinafter referred to as a “flexible circuit substrate”) is disposed between a semiconductor package and a circuit substrate.
An example of the above-described related art is disclosed in Japanese Laid-open Patent Publication No. 2011-103441.
In the above-described electronic apparatus, through-holes are formed in the flexible circuit substrate, and electrodes of a semiconductor package and electrodes of a circuit substrate (for example, a printed wiring board) are connected to each other via bumps which pass through the through-holes. Then, by using these bumps, the flexible circuit substrate is fixed to the circuit substrate.
However, before the flexible circuit substrate is fixed by using the bumps, it is likely that the flexible circuit substrate will be tilted or displaced if a slight force is applied or the flexible circuit substrate is thermally expanded during a reflowing process.
If the flexible circuit substrate is tilted, a connection fault may occur in bumps which connect the flexible circuit substrate and the semiconductor packages. If the flexible circuit substrate is displaced, a connection fault may occur in bumps which connect the flexible circuit substrate and the circuit substrate.